The present invention relates to a process for the preparation of fat-containing milk powder.
In the preparation of milk powder, it is economical to concentrate production in regions where fresh milk is available in great quantities and at an economic price. It is thus desirable to increase the capacity of existing installed drying equipment, particularly spray drying towers, without investing in new equipment. A means to achieve this goal would be to introduce highly concentrated milk into the drying step. A problem is that in treating of highly concentrated milk product quality deterioration occurs as a consequence of fat clustering of the highly concentrated milk mainly during homogenization. Homogenization cannot be omitted because of the poor solubility of powders made from non-homogenized milk.
U.S. Pat. No. 5,518,751 discloses a process for the manufacture of recombined evaporated milk concentrates and milk powders by introducing a vegetable fat into the liquid concentrate in the course of evaporating for increasing the unsaturated fatty acid content thereof. In an embodiment for making milk powder, after introduction of the fat in the last effect of the evaporator, the mixture is homogenized before being dried.
EP-A-0 627 169 discloses a process for the manufacture of liquid evaporated milk in which the preheating and evaporation steps are within the evaporation equipment and homogenization takes place before concentration.
EP-A-0 873 690 discloses a process of preparing a fat-containing foodstuff comprising adding a fat phase to an aqueous phase said adding and homogenizing being located between two evaporators of a plurality of evaporator effects. The purpose of this step is to protect heat-sensitive oils. For instant milk powder it would not make sense to separate the fat from the production milk prior to evaporation.
Thus, there remains a need for an improved process for preparing a fat containing mild powder.
We have found that it is possible to drastically increase productivity of manufacture of milk powder by primary spray drying fresh milk and by the way to maintain or even improve the powder quality in that homogenization is carried out at mid way of evaporation, i.e., on the pre-concentrate between the stages of the multiple stages evaporator. This positioning of homogenization in the present invention is a solution to the problem of too high viscosity obtained in a concentrate homogenization. Thus the control of viscosity allows drying of the concentrate to a solids content of 50% by weight or greater without adversely affecting the quality of the powder obtained after drying.
The process of the invention thus comprises preparing a standardized milk, feeding the prepared standardized milk into an evaporator having at least one stage to obtain a pre-concentrate, homogenizing the pre-concentrate, further evaporating the pre-concentrate in an evaporator having at least one stage to obtain a concentrate having a total solids content of at least 50% by weight, and then spray drying the concentrate.
Preferably, the pre-concentrate is homogenized in two stages, with the preconcentrate is homogenized in a first stage at a pressure of from about 50 to about 250 bar and then in a second stage at a pressure of up to 150 bar. Also, the milk concentrate can be spray dried using high pressure swirl nozzles, at a pressure of about 140 bar.
The resulting spray dried milk can be agglomerated and instantized by lecithination, after-dried, after-cooled, filled into packs and gassed. Preferably, the liquid milk is recombined from milk powder, skim milk powder, butter oil or vegetable oils along with an appropriate amount of water.